Switching technologies are very important to network design because they allow traffic to be sent only where it is needed.
A data link layer is layer 2 of the seven-layer Open Systems Interconnection model (OSI model) of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model. The data link layer is the protocol layer that transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network segment. The data link layer provides the functional and procedural means to transfer data between network entities and may provide the means to detect and possibly correct errors that may occur in the physical layer. Examples of data link protocols include Ethernet for local area networks (multi-node) and Point-to-Point Protocol (PPP).
In general, layer 2 switching is hardware-based, which means it uses media access control address (MAC address) from a host's network interface cards (NICs) to decide where to forward frames. Switches may use application-specific integrated circuits (ASICs) to build and maintain forwarding tables (also known as MAC address tables). A layer 2 switch may be considered to be similar to a multiport bridge.
In computer networking, network address translation (NAT) is a process for modifying IP address information in IP packet headers while in transit across a traffic routing device.
On devices that use ASICs to switch packets at layer 2 of the OSI model, one way to implement NAT is to process packets in the CPU or to add an FPGA component to achieve line rate performance. However, due to the layer 3 nature of NAT, packets flowing across a NAT boundary from one IP sub domain to another while maintaining the same layer 2 domain structure may lead to breakdown of conventional communication between network nodes. This is mainly because a protocol such as Address Resolution Protocol (ARP) may not work as expected in this scenario.
Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.